Fraudulent calls, such as well-known "blue box" and "black box" calls, cost telephone companies, particularly interconnect carriers, huge financial sums both in lost revenue for those calls and in the payment of access charges for those calls to local exchange carriers.
The concurrently filed application of R. L. Else and K. D. Frantzen describes a toll fraud control feature for disabling communications on the transmit path of a four-wire call connection until a valid call answer signal is received and verified at a controlling office to bill the user for the call. That arrangement frustrates "blue box" access and satisfactorily precludes "black box" calls from being completed through the network.
However, the toll fraud control arrangement does not differentiate between legitimate and fraudulent calls and disables communications on the transmit path of every call passing through a switching system. Until valid answer supervision is received for the call, communications on the transmit path remain disabled. As a result, customers attempting to place legitimate calls through the interconnect network to a called line having faulty equipment or a "black box" connected thereto will not have their calls completed. Prevented from completing a call, a caller attempting to place a legitimate call will typically seek the assistance of an operator to complete the call for the caller. However, the problem is that an operator, like the customer, will encounter disabled communications on the transmit path for the call due to the toll fraud control arrangement and will not be able to assist the customer and to bill the customer for the call.